Many types of spinal irregularities cause pain, limit range of motion, or injure the nervous system within the spinal column. These irregularities can result from, without limitation, trauma, tumor, disc degeneration, and disease. Often, these irregularities are treated by immobilizing a portion of the spine. This treatment typically involves affixing a plurality of screws and/or hooks to one or more vertebrae and connecting the screws or hooks to an elongate rod that generally extends in the direction of the axis of the spine.
Treatment of these spinal irregularities of involves using a system of pedicle screws and rods to attain stability between spinal segments. Instability in the spine can create stress and strain on neurological elements, such as the spinal cord and nerve roods. In order to correct this, implants of certain stiffness can be implanted to restore the correct alignment and portion of the vertebral bodies. In many cases, an anchoring member such as a pedicle screw along with vertical solid member can help restore spinal elements to a pain free situation, or at least may help reduce pain or prevent further injury to the spine.
It is well known that difficulties can arise during a surgical procedure when attempting to connect a vertical solid member, such as a rod, to a bone screw. As a result, it may be desirable to use a variable angled coupling element to connect a rod to a bone screw. This lessens the need to modify the system such as by bending the rod, by repositioning the screw, or the like. The coupling element acts as an elbow which can reach out to the rod and allow for easier adjustment and installation of the rod in the patient.
Typically, a conventional polyaxial screw often has a cap of some kind used to compress the rod onto the coupling element. This compression of the rod enables the locking mechanism within the coupling element to fix the angle between bone screw and said element. Although polyaxial screw systems are prevalent, the polyaxial screw also cause some issues during placement. For instance, the polyaxial screw system allows a full range of motion that makes it difficult to place correctly within the bony elements of the spine. Furthermore, the accuracy required by the doctor to position the polyaxial screw is paramount and fluctuations due to the mechanical aspects of the polyaxial screw may compromise the accuracy in positioning of the polyaxial screw. Thus, there is a need for a screw system that limits the motion of the screw system during placement of the screw and provides superior fixation in the bony elements of the spine.